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heterogeneous catalysts: catalyst is in different phase from reaction mixture

homogeneous catalysts: catalyst is in the same phase as reaction mixture

- example is iron in haber process (N2(g)+3H2(g)->2NH3(g) using Fe iron powder in solid form)

Heterogeneous Catalyst

• normally involve gas molecules

• catalyst is usually solid

• use surface of catalyst as site of reaction

• mechanism of catalyst can be explained by using theory of absorption

• diffusion to surface: the nitrogen and hydrogen will diffuse towards the catalyst

• adsorption: form bonds with catalyst

• reactions: bonds between hydrogen - hydrogen and nitrogen - nitrogen will weaken and bonds will form between nitrogen and hydrogen

• desorption: break bond with catalyst

• diffuse away from catalyst

Homogeneous Catalyst

• involve changes in oxidation catalyst

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Reflection notes
Heterogenous catalyst info
1. it is in different phase from the reactant
2. steps include diffusion, absorption, reaction, desorption.
Homogenous catalyst info
1. same phase as reactants
2. change in oxidation number
Need to revise graphs part and pyp

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-A heterogeneous catalyst is a catalyst that is in a different phase as the reaction mixture. Three main steps involved in the mode of action of a heterogeneous catalyst are, adsorption, reaction, and desorption.

-homogeneous catalysts are in the same phase as the reaction mixture. Changes in oxidation number of the ions involved in the catalysis occurs. Transition elements often make good catalysts as most of them have the ability to change oxidation numbers.

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Rate-determining Step
- Usually the first step
- Slowest
- Rate of reaction equation is dependant on it
- Follow stoichiometry equation for multi-step equation

Homogenous Catalysis
- In phase : There is a same state in reactant & product [(aq) --> (aq), etc. ]
• (l) is considered same as (aq)
- Oxidation number : There is change in oxidation number between reactant & product
• Usually a 2-step equation
• Catalyst is used up in 1st step, and comes back in 2nd step

Heterogeneous Catalysis
- Diffusion towards the surface --> Absorption --> Reaction --> Desorption --> Diffusion away from surface
- Used in catalytic converters

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What i learnt:

[ ] - t graph of 0,1,2 order

rate - [ ] graph of 0,1,2 order

t 1/2 is constant for 1st order ( [ ] - t graph)

rate determining step is the slowest step

only substances that take part in the rate determining step appear in the overall rate equation ( rate = k[X]^m[Y]^n)

T increase, rate increase, k increase

heterogenous catalyst is in a different phase to the reaction mixture (mechanism: theory of adsorption/Chemisorption)

Adsorb: bond to the surface of the substance

Absorb: move into the substance

hetero cat steps: 1) diffuse to surface 2) adsorption 3) reaction 4) desorption 5) diffuse away from surface

homogeneous catalyst is in the same phase as the reaction mixture

homo cat used in one step, reformed in another

homo cat involve changes in oxidation number

enthalpy change - progress of reaction graph of SN1 mechanism (first step is slow, formation of carbo cation)

SN1 graph - intermediate is in the middle of the two humps

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what i learnt:

heterogeneous catalysis involves gaseous molecules acting at the surface. it only occurs when the catalyst is in the same phase as the reaction mixture. it involves adsorption (weaking of bonds within reactants), reaction, and desorption(breaking of bonds between products and catalyst). example of this would be the the palladium,platinum,and rhodium in the catalytic removal of oxides of nitrogren from exhaust gases of gar engines, or even iron in haber process. homogenous catalyst occurs when the catalyst is in the same phase as the reactants. it involves the changes in oxidation number. rate of reaction depends on the slowest step. energy profile diagram has two humps for activation energy.

areas i need to study more:

i will need to practice more pyp questions and do more worksheets to familiarize myself with the chapter more

the teaching was great as usual, it was very detailed and easy to understand.

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I learnt about the importance of the rate determining step, about homologous catalysts and also heterogenous catalysts. With homologous the catalyst is in the same state as the reactants and there will be redox reactions. While in heterogenous the catalyst is in different state than its reactants where adsorption will happen. I also learnt about the importants graphs(concentration,time),(rate,concentration) and how to determine the order. Lastly in concentration,time graph i can determine the first order from the second order if half time is constant.

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I learnt about different types of catalyst, homogenous and heterogenous. Homogenous means same phase as the reaction mixture and heterogenous is the opposite of homogenous. I also learn about the rate determining step

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rate determining step

the first step is normally the slowest step

rate of reaction equation depends on the slowest step

rate equation follows the stoichiometry equation for multi-step reaction

homogenous catalyst

same phase as reaction mixture involve changes in oxidation number

changes N₂ to NO or NO₂ using lighting

used in car engine

can form intermediate step (energy profile diagram has double bump)

heterogeneous catalyst

different phase as reaction mixture

mechanism explained using theory of absorption

absorb (move right into the substance)

used in catalytic converters (rhodium catalyse the reduction of NO to N₂)

steps:
1. gas molecules diffuse to the surface
2. absorption (bond to the surface of the substance)
3. reaction (new bonds forming)
4. desorption
5. diffusion away from surface

As usual, the lesson was clear and easy to follow. The examples given from the past paper also helped a lot in helping me understand the chapter. However, I will still need to practice more questions.

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Rate of Reaction

rate constant changes with temperature

rate determining step is the slowest step in a multistep reaction

for multistep reaction the rate equation follows the stoichiometric equation

Heterogeneous Catalyst

catalyst is in a different phase from the reactants

adsorption (chemisorption): weakening of bonds within reactants, forming of new bonds with the catalyst

desorption: breaking of bonds between products formed and the catalyst used

examples: iron in the haber process, and palladium, platinum, or rhodium in catalytic converters

Homogeneous Catalyst

catalyst is in the same phase as the reactants

involves changes in oxidation number

catalyst is used up at first, then re-formed later on

examples: oxides of nitrogen in the oxidation of sulfur dioxide, and Fe²⁺ or Fe³⁺ in the reaction between iodide and peroxodisulfate ions

Energy Profile Diagrams

two humps for activation energy indicates a two-step reaction (involves formation of a stable intermediate/carbocation)

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I finally understand the rate-determining step!!! Allow me to divulge ! ! ! my information ! ! !!

- The rate-determining step is the slowest step, and is often the first step.
- All the reactants in the rate-determining step is also in the rate equation, their orders determine how many mols are to be involved in the step. These two conditions must be fulfilled by the rate-determing step.
-  For example- r =(k) (a^2)(b^1)
2a + 1b -> bla bla bla
- If there are reactants that are not in the rate-determining step BUT are in the overall equation, they will be involved in the second, third, etc. steps.
- Intermediates formed by the first step (but not in the overall equation) will be used up in the next steps!

Homogenous Catalysts:
- involved in the reactions
- change in oxidation states, but at the end of the reactions its o.s. remains the same.
- lowers the activation energy this way, by separately reacting with the reactants instead of the reactants reacting together (sometimes bc of similar negative charge)
- changes the energy profile to usually 2 lower bumps, pertains to SN1.

Heterogenous Catalysts:
- Different Steps:
1. Diffusion: reactants diffuse towards the catalyst
2. Adsorption: REMEMBER it's STICKING to the catalyst, not like,,, going through it
3. Reaction: bonds within the reactants weaken (like, within the nitrogen molecules) , bonds strengthen between the reactants molecules (like, between the hydrogen and nitrogen molecules)
3. Desorption: reverse adsorption basically (bonds formed between the reactants and the catalyst break)
4. Diffusion: products diffuse away from the catalys

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We revised about homogenous and heterogenous catalyst and how they work. and learnt about the rate determining steps furthermore we learnt about order of reactions using graphs energy profile diagrams and absorption and adsorption

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I learnt about the different catalysts, and the reactions that are associated with these different reactions. I also learnt that the slow reaction determines the rate.

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Rate determining step is the slow step

Reactants in the slow step must be included in the rate equation

Homogenous catalysts

occurs when the catalyst is in the same phase as the reaction mixture

reactants, products and catalyst are all in the same state

involves changes in oxidation number

example: nitrogen oxide and acid rain, iodine and peroxodisulfate

Heterogenous catalysts

occurs when the catalyst is in a different phase to the reaction mixture

catalyst is in the solid phase, whereas the reactant is in aqueous state

involves gaseous molecules reacting at the surface of a solid catalyst

The mechanism of the catalyst can be explained using the theory of adsorption (when the reactant is chemically bonded to the surface of the substance)

Steps: diffusion to the surface, adsorption, reaction, desorption, diffusion

Example: iron in haber process, catalytic converters

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Rate determining step

Overall rate of reaction depends on the slowest step

If a substance does not appear in the overall rate equation, it does not take part in the rate determining step (slowest step in multi-step reaction)

Rate = k [reactant in slow step] ; then follow the stoichiometry/mole ratio

mole/stoichiometry use it to determine the order of the reaction

Homogeneous catalyst

When the catalyst is in the same state with the reactant

Involves changes in oxidation number

Energy is needed more (activation energy is high) without homogeneous catalyst

as in order to collide and react, these ions need considerable energy to overcome the repulsive forces when like charges approach each other

With homogenous catalyst, creates an alternative pathway with lower activation energy

Graph SN1 mechanism, has reactant → intermediate → product

Heterogeneous catalyst

When the catalyst is in different state with the reactant

Often involves gases molecules reacting at the surface of a solid catalyst

Mechanism of catalyst can be explained using the theory of adsorption

Adsorb means

Bond to the surface of the substance

Move right into the substance

1. Diffusion to the surface

2. Adsorption :

1. reactant molecules are chemically adsorbed onto surface of ions

3. Reaction

4. Desorption : release of product molecules from the surface of heterogeneous catalyst

5. Diffusion

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I learnt about :
- In a multi step reaction, we use the slow step to write the rate equations because the slow step is the rate determining reaction.
- We use the number of moles in the reactants as the order of reaction in each concentration.
- Homogenous Catalyst :
• Same phase as reactants. Involve change in oxidation number.
•Produces intermediate and energy profile diagram will have two humps.
- Heterogenous Catalyst :
•Different Phase with reactants
• Mode of Action (Diffusion, Adsorb, Desorption)

What to improve on:
- I need to improve on how to determine which is the slow step.

Comments :
-Lecture was very organized and clear. Very easy to understand.

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We revised on the 2 different types of catalyst which are homogenous catalysts and heterogenous catalysts. We also learnt about the different types of reactions and usages of these two types of catalysts. Furthermore we also reviewed on the Nucleophilic Substitution graphs of SN1 and SN2. Another thing that we learnt is about the rate determining step which is the slowest step of a reaction.

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Rate-determining Step

Slow step of reaction (usually in the beginning)

Determines rate equation

Rate equation follows stoichiometric equation of slow step

Homogeneous Catalyst

Ester hydrolysis (H+ aq)

H2O2 breakdown (I- aq)

S2O8 2- + 2I- → 2SO4 2- + I2 (Fe 3+)

Changes in oxidation number, but catalyst reformed

Heterogeneous Catalyst

Haber process (Fe)

Catalytic converters (Pt)

Steps:

1. Diffusion and adsorption

2. Reaction

3. Desorption

4. Diffusion away

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Revised:

catalysts (homogenous and heterogenous)

examples of use of homogenous and heterogenous catalysts:

iron in the haber process; catalytic converters

iodine and peroxodisulfate

SN1 and SN2 energy profile diagrams

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Reviewed on:

- The graph for the energy profiles of SN1 and SN2

-Homogeneous catalyst refers to where the catalyst are in the same phase

-Heterogenous catalyst refers to where the catalyst are in different phases

-The rate determining step of a reaction depends on the stoichiometry of the slowest reaction.

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- The slow reaction is the rate-determining step in the overall reaction.
- Homogenous & Heterogenous catalysis.
- Homogeneous, the reaction mixture is the same phase as the catalyst. (change in oxidation number)
- Heterogenous, the reaction mixture is in a different phase as the catalyst. (theory of adsorbtion)
- The energy profile diagram for SN1 and SN2

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I learned about homogenous, heterogenous (and their examples) and different catalyst types. I also learned about adsorption and absorption as well as more in-depth on multi step reaction as well as sn1 and sn2 energy profile diagrams

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From today's lecture, I learnt about the following:

- Rate-determining Step

rate of reaction depends on the slowest step

intermediates formed by first step will be used up in the next step

rate equation can be determined by the rate-determining step

in a multistep reaction, the number of moles present in the reactants of the equation is used as the order of reaction for the concentration, in other words the rate equation follows the stoichiometric equation

- Two different types of catalyst (homogeneous and heterogeneous)

- Homogeneous Catalyst

same phase, so reactants, products and catalysts are all in the same state

involves changes in oxidation number

nitrogen oxide & acid rain  (NO2)

iodide ions and peroxydisulfate (Fe3+ ions)

- Heterogeneous Catalyst

different phase (usually when the catalyst is in the solid phase, whereas the reactant is in aqueous state)

steps include diffusion to the surface, adsorption, reaction, desorption, and diffusion away from the surface

haber process (iron)

catalytic converters (platinum, palladium, rhodium)

- Energy profile diagram for SN1 and SN2 mechanism

Overall, it was a great and enjoyable lecture as usual — the discussions and points were clear and concise, so it was not that hard to follow along. I believe that I just need to revise some more past year paper questions before I can fully understand this chapter.

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Learnt about:
- Rate determining step
- it depends ont he slowest reaction/step
- Will have the reactants in the step

Homogeneous catalyst:
- changes in oxidation number
- is in the same state as the reactants (usually aqeous)

Heterogeneous
- Usually a solid catalyst with gas reactants and products
- Acts as a medium for the fgas molecules to bond

The lesson was easy to understand with the examples.

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The rate determining step depends on the slowest reaction, this does not include intermediates.

Homogeneous catalyst changes the oxidation number and can help react due to different charge signs and it has to be in the same phase.

Heterogeneous catalysts provide a surface for the reactants to react in a different phase. (Iron in haver process)

We also learnt about the energy profile diagrams of Sn1 and Sn2 reactions

The lesson was good and I think no improvements really need to be made.

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- rate determining step is the slow step (high activation energy)
- Rate equation shows the reactants in rate determining step
- homogeneous catalyst -> same phase
can be seen through change in oxidation number (S2O82-, nitrogen oxide & acid rain)
- heterogeneous catalyst -> different phase (haber process & catalytic converters)
- energy diagram of sn1 and sn2 reactions
- need to do more pyp practices

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Reviewed on:
-Rate determining step and that the slow step will always involve the order of reactions through stoichimetry
-Order of reaction of concentration-rate and concentration-time graph
-Reactants that are not found in the slow step is not used in the overall equation
-Catalysis of homogenous and heterogeneous catalyst
-Homogenous involves change in oxidation number
-Heterogeneous involves the theory of adsorbtion

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Learnt:

-The rate-determining step is the slowest reaction in the overall reaction.
- There are 2 types of catalyst: Homogeneous and heterogenous catalyst
- Heterogenous catalyst is when the catalyst is a different phase than the reactant
-Homogenous catalyst is when the catalyst is in the same phase as the reactant
- The energy profile diagram for SN1 and SN2

The lecture was clear and I need to practice more on the calculation

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- Homogenous & Heterogenous catalyst and their different phase and mechanism
* Homogenous -Same Phase
* Heterogenous - Different Phase

- Temperature increase , rate also increase because of K (rate constant) [increase]

To do / more practice :
- Do pyp more

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Learnt:

rate determining step is slow step

two types of catalyst: homogeneous and heterogeneous

heterogeneous catalyst is in different phase, use chemisorption mechanism

homogeneous catalyst is in same phase, involves change in oxidation number

lecture was clear.

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During the lecture, i learnt about reaction kinetic graphs of the three order reactions.

I learnt that in rate equations, when temperature increases, rate increases also because of the increase of K (rate constant).

then i also learnt about rate determening step and practiced some questions.
(How to deduce reactions, find overall rate equation, calculate initial rate of reactions, etc)

(Step 1 is usually the slow step and must have the reactants)

Lastly, i reviewed on homogenous and heterogeneous catalyst.

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Rate determining step depends on the slowest reaction, this does not include intermediates.

Homogeneous catalyst
Changes oxidation number and can help react due to different charge signs

Heterogeneous catalyst
this provides a surface for the reactants to react (for example iron in haber process)

energy profile diagrams of Sn1 and Sn2 reaction

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Rate determining step

overall rate of reaction depends on the slowest step

If a substance does not appear in the overall rate equation, it does not take part in the determining step

Two types of catalyst

Homogenous catalyst: catalyst is in the same phase as the reaction mixture

Heterogenous catalyst: catalyst is in different phase as the reaction mixture

Heterogeneous catalyst

involves gases molecules reacting at the surface of a solid catalyst

Mechanism can be explained using the theory of adsorption

Carbon monoxide will react with oxygen and oxidize to form carbon dioxide. Catalytic converters does not stop global warming but they try to convert carbon monoxide and nitrogen oxide to something less harmful.

Homogenous catalyst

atmospheric oxides of nitrogen in the oxidation of atmospheric sulfur dioxide

Intermediate is something that will be used up in the next reaction such as IO-

Nitrogen is not very reactive because of the triple bond.

No2 act as a catalyst for thunderstorm reaction

Energy profile diagram

Sn1 is going to have two humps while Sn2 will only have 1

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Learnt about:
Rate determining step.
The slower step will affect the rate equation.
Reactant that is not used in rate determining step will not be included in the rate equation.
Use rate equation to determine the steps of a reaction.
Homogenous catalyst and heterogenous catalyst.

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Reviewed on :
- rate determining step, which is the slow step
- order of reaction’s graphs
- homogeneous and heterogeneous catalysts
- energy profile diagrams
- absorption vs adsorption

Need to practice more on :
- energy profile diagrams
- order of reactions

The teaching was provided with brief descriptions and was understandable.

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Learnt:
- Rate determining step
slow step is always the first step, etc...

- Homogenous catalysts
Catalyst reacts with the reactants and splits the reaction into two steps. Gets oxidized and reduced but no overall change

- Heterogenous catalysts
Reactants bond with the surface of the catalyst, weakening the bonds within themselves. Once the bonds in the reactants are broken and they are bonded with the catalyst, the reactants start bonding with each other and them break the bond with the catalyst and leave.

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- rate determining step
- depends on slowest step
- need to appear in rate equation
- homogeneous and heterogeneous catalyst
- heterogeneous diffusion/adsorption/desorption
- homogeneous catalyst change oxidation number
- SN1 2 humps reaction SN2 1 hump